Cerebral ischemia is the third leading cause of death in this country and is a feared perioperative complication. As cellular and molecular understanding of the pathophysiology of ischemic brain injury emerges, new treatment possibilities are being discovered. The use of endogenous stress proteins to protect the brain has been under study for some time and is a promising candidate strategy. In their previous funding period, the investigators were able to demonstrate that hsp70 alone was as effective as a heat pretreatment in protecting brain cells from subsequent ischemia like insults. They will now pursue this treatment possibility in three ways. First, by carrying out studies in transgenic mice to determine the effect of increased hsp70 expression in vivo; second, by pursuing gene therapy in vitro using hsp70 over expressing astrocytes, and third, by determining the range of protection provided by another stress protein important in protection from oxidative injury, hsp27. 1) Focal cerebral ischemia will be performed on hsp70 transgenic mice, homozygotic transgenic, heterozygotic and non-transgenic littermates. The extent of injury will be determined with magnetic resonance imaging (MRI) and histology, volumes of infarction will be calculated. 2) If protection is found, the mechanism will be pursued by determining the number of apoptotic cells for each genotype, to see if fewer apoptotic cells are detected in the transgenic mice. 3) The mechanism of neuronal protection by hsp70 overproducing astrocytes will be studied as one model for gene therapy. 4) The mechanism of protection will be sought by determining levels of glutamate in protected cultures deprived of oxygen and substrate compared to controls. 5) The extent of protection against neuronal injury will be compared in cultures over expressing hsp70 in astrocytes or neurons or both cell types. 6) Over expression of hsp27, another stress protein, will be tested for its ability to provide brain cell protection from three different insults. This stress protein is known to stabiize the cytoskeleton, and may prove beneficial in the setting of cerebral ischemia where cytoskeletal disruption occurs. The knowledge gained from this project has direct implications for the treatment of ischemic stroke in both surgical and medical patients.